Hi there,
I'm not going to talk about the type of the musics here but I'm talking about having less lag by using the suitable musics.
each time you play a music in your computer the CPU has to analyze whole music first then starts to play,so if the music is to long it takes more time to analyze it.(if your not doing anything you'll see no difference but while playing a game with more than 85% of CPU usage you feel it is taking more time).
So if you are a game developer and you want less lag for low spec systems try using shorter musics rather than long ones,as we know the musics have loops so do not make a loop while making a music and let the game engine to do it.
For example I downloaded a music for one of my games and I saw it is repeating the same notes each 10 seconds and the music was 5 minutes,so I just copied the first 10 seconds and removed the rest of it.
Here is a very easy way to do this whit windows movie maker(I used WMM because it is on your windows and it's free):
After opening the program you'll see this page:
Then just as shown in the image just click on import audio or music the just import your music from the new window which is like the image below:

Then as it said just drag and drop it on the storyboard:

Now just do as it says in the image:

Wait until the time you need to cut the music or just use the timeline then pause the music and just press CTRL+L to cut the music.
It will be like this:
then just click on the part you don't want and press Delete key to remove it.
Now just press Ctrl+P and save your edited music where ever you want.
Now your music is ready to use in FPSC.
I hope you enjoyed.
Have our guns was a mistake!!!
I am PaYaM